Process of preparing dihydroxybenzenearsonic acids



benzene nucleus, are obtainable by treating with Patented May 7, 1 935 2,060,351 i PaocEss or mmimanmmnox -y I BENZEIQEARSONIC ACIDS Karl streitwolf, lFrankfort-on-the-Main, and

Alfred Fehrle, Bad Soden-on-the-Taunus, and Hans Hilmer, Frankfort-on-the-Main, Germany, assignors to Winthrop ChemicahGom-' vpany, Inc., New York, N. Y., a corporation. of

New York No Drawing. Application May 8, 1931, Serial No. 536,078. In Germany May 26, 1930 v wann ,(Gl.2 -14)1 paper. By pouring it"into acetone the monosodium salt. of thepyrocatechinarsonic acid is isolated.- The salt has the following formula:

UNITED STATE The present invention relates to a process of preparing dihydroxybenzenearsonic acids.

We have found that ihydroxybenzenearsonic acids which may. be further "substituted in the oxidizing agents a compound of the Iollowing eneral formula; I

(2) 1/10 mol. of arsonic aoid-pyrocatechincarbamic acid ester (of. our co-pendingU. S. application Ser. No. 535,804 filed May 7, 1931) is saponified by means ,otitimes its weight of 3N- hydrochloric acid; alkali is addeduntilthe solution is feebly alkaline to turmeric and the solution containing the sodium salt of 3.4-dihydroxybenzene-I-arsonm; acid is then reduced by means of sodium hydrosulfitew The 'iurther treatment is carried out' as indicated'in-Example l. s

(3) 1 /10 mol. of hydroxy -phenylarsoni'c acid is oxidized :,by means: of potassium persulfate according to the 1 process of German Patent No. 271,892, dated November 13, 1912, filed in the name of Farbwerke vorm. Meister Lucius 8: Briining. j After oxidation "boiling with hydrochloricacid th'e' wholes is neutralized by means of alkaliand the solution thus obtained is reduced by means of hydrosulfite to the arseno-. benaenedronxwhich the pyrocatechinarsonic acid can be obtained in the manner indicated-231l ve;

(4) 5 grams of the arseno-dipyrocatechindiethylcarbamic acid ester, obtained by reduction of the corresponding arsonic acid (of. our copending U. S. application referred to in Example 2) are heated on the steam bath with 10 cc. of caustic potash solution of 37 B. until the evolution of diethylamine is complete. The whole is then diluted withso much water that the solution can easily be filtered. On acidifying with acetic acid the tetra-hydroxy-arsenobenzene separates. It is oxidized to the pyrocatechinarsonic acid as indicated in Example 1;

(5) 36 grams of tetrahydroxyarsenobenzene are suspended in 200 cc. of water and the suspension is mixed with normal iodine solutionuntil a sample of the mixture just colors potassium iodide starch paper. On the addition of the iodine, the insoluble matter is dissolved and a colorless liquid is produced. It is filtered after addition of animal charcoal and the strongly acid filtrate is rendered neutral by means of caustic (OI-l)gAr--As=AsAr--( OH): wherein stands for a benzene nucleus may be fu'rther substituted. I g

The process is preferably carried out bytr eating an aqueous suspension of thearsenobenzene compound with oxidizingagents, as tor instance, with hydrogen peroxide or'a solution of iodine in an amount which is suflicient to oxidize the arsenic atoms to arsonic acid groups. Hereby the arsenobenzene is oxidized to the corresponding arsonic acid which is, immediately dissolved in the water present during the oxidation process. The arsonic acid may be obtained from theaqueous' solution in known manner, for instance, bylevap crating thesolution. It can be further purified by dissolvingthe residue in water, neutralizing the solution thus obtained with caustic soda solution and pouring itinto acetone, whereby the sodium salt of the arsonic acid crystallizes.

Thepr'ocess can advantageously be utilized for separating the dihydroxybenzene-arsonic acid in a pure state and with a good yield from the reaction mixture in such processes by which the said acid was directly obtainable up to the present time only in a more or less contaminated form and with a small yield. In such a case the reaction mixture containing the dihydroxybenzenearsonic acid is treated with a reducing agent and the tetrahydroxyarsenobenzene which after isolation is obtained thereby free from impurities is oxidized as above indicated.

The following examples illustrate the invention, but they are not intended to limit it thereto.

(1) 1/20 mol. of 3,4,3,4',-tetrahydroxy-arsenobenzene is triturated with 3-5 times its weight of Water and oxidized while cooling and stirring, with hydrogen peroxide. The solid matter is dissolved; the solution is purified with animal charcoal and then evaporated in a vacuum. The residue is taken up in a small quantity of water, filtered through animal charcoal and mixed with caustic soda solution until it is neutral to litmus wh c soda solution. The mono-sodium salt of the pycharcoal and concentrated until the nitropyro-Q catechinarsonic acid begins to separate. The

yield amounts to about 17 grams. Theiacid the following formula:

g .7 HOQ- "on OIN We claim:

1. The process which comprises treating a compound of the following general formula wherein 'Ar stands for a benzene nucleus which may be further substituted by a nitro group with' a mild oxidizing agent in an amount sufficient to oxidize the arsenic atoms to arsonic acid groups. a

V 2. The process which comprises treating a compound of the following general formula wherein X stands for a substituent of the group consisting of hydrogen and nitro, with a mild oxidizing agent in an amount sufficient to oxidize the arsenic atoms and arsenic acid groups.

3; The process which comprises treating a compound of the following formula in an amount sufllcient to oxidize "the arsenic atoms to arsonic acid groups with a mild oxidizing agent.

' compound-ofthe following formula:

4. The process which comprises treating a compound of the following formula HO OH in an aqueous suspension with hydrogen peroxide in an amount sufficient to oxidize the arsenic atoms to arsonic acid groups, evaporating the solution thus obtained and, if required, purifying the product thus obtained by dissolving it in wa ter," clearing the solution by addition of charcoal and-by filtration, neutralizing it by addition of caustic soda solution and pouring it into acetone.

5. The process which comprises treating a compound of the following general formula HO OH I OzN NO:

with 'afmild oxidizing agent.

. 6. The process which comprises treating a compound of the following general formula HO OH in an aqueous suspension with hydrogen peroxide, evaporating the solution thus obtained and, if required, purifying the productthus obtained by dissolving it in water, clearing the solution by addition of charcoal and by filtration, neutraliz ing it by addition of caustic soda solution and pouringit into water.

"7. The process which comprises treating a in an aqueous suspension with iodine solution until a, sample of the mixture just colors potas- 4 siiun-iodide-starch-paper, clearing the solution 7 by addition of charcoal and filtration, neutralizing it- 'and' precipitating the monosodium salt of I pyrocatechinarsonic;acid with acetone.

KARL STREI'I'WOLF. ALFRED FEHRLE. HANS HILNIER. 

